Approach for Predicting Formation of Fine Grain Layers in Metal Forming

This paper examines the possibility to use the strain rate intensity factor for describing the formation of fine grain layers in the vicinity of frictional interfaces in metal forming processes. This factor controls the intensity of the equivalent plastic strain rate in a narrow zone near such interfaces. The layer of intensive plastic deformation is identified with the layer of fine grains. Dimensional analysis is carried out based on the assumption that the increase in the thickness of the layer of intensive plastic deformation at a point of the friction surface depends on the strain rate intensity factor and its thickness at this point. An approximate value of the strain rate intensity factor in the process of plane strain extrusion is determined from a semi-analytic solution. Preliminary experiment is carried out on a copper sheet. As a result, a specific relation for calculating the thickness of intensive plastic deformation in the copper is found.